交易成本（英语：Transaction Cost）是一个经济学概念，指完成一笔交易时，交易双方在买卖前后所产生的各种与此交易相关的成本。在1937年科斯（R.H.Coase）提出的论文－〈The Nature of the Firm〉（公司的本质），被视为是交易成本理论的奠基者。经济学家张五常认为，Transaction Cost应译作交易费用而非交易成本。

以国际贸易为例，列举如下：

In economics and related disciplines, a transaction cost is a cost incurred in making an economic exchange (restated: the cost of participating in a market).

Transaction costs can be divided into three broad categories:

For example, the buyer of a used car faces a variety of different transaction costs. The search costs are the costs of finding a car and determining the car's condition. The bargaining costs are the costs of negotiating a price with the seller. The policing and enforcement costs are the costs of ensuring that the seller delivers the car in the promised condition.